Chronically instrumented (electrodes, vascular and tracheal catheters) fetal Rhesus monkeys will be used to investigate fetal cardiovascular and metabolic responses to hypoxic and other stresses. Microspheres will be used to detect changes in blood flow distribution. The effect of autonomic agonists and antagonists on stress induced changes in blood flow distribution will also be studied. In addition, the fetal plasma levels of adrenocortical steroids and estrogens will also be measured in relation to stress and the onset of labor. Feedback relationships affecting the fetal thyroid will also be investigated. BIBLIOGRAPHIC REFERENCES: Murata, Y., Martin, C.B., Jr., Miyake, K., and Ikenoue, T.: Systolic Time Intervals of the Cardiac Cycle in Fetal Rhesus Monkeys - Ventricular Ejection Time. Gynec. Invest. 8:107, 1977. Murata, Y., Martin, C.B.: Systolic Time Intervals of the Fetal Cardiac Cycle as Indications of Fetal Cardiac Function. Postgrad. Med. 61:127, 1977.